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New hydrogel can ‘walk’ in water by changing temperature

Scientists have developed a new hydrogel that was able to “walk” in water and air and can change shape faster than existing polymers.

Hydrogels are polymers known for their ability to hold large quantities of water. They can swell and shrink in response to changes in the environment — such as voltage, heat, acidity and temperature. These gels resemble plant cells, which change shape depending on the amount of water they hold.

These polymers are malleable, flexible, durable yet it’s mostly made of water. Hydrogels already have numerous applications such as used in disposable diapers and moisturizing cosmetics. Hydrogels are used as dressings for wounds. There is research to develop these polymers for drug delivery and cartilage repair.

Normally, the expansion and shrinking of hydrogels as they absorb or release water is a slow process. The team led by researchers at RIKEN Center for Emergent Matter Science in Japan wanted to accelerate that process.

The researchers were able to modify the new hydrogel to only contract in one direction while expanding in another. This modification meant that the hydrogel did not need to absorb or expel water to move. Then, the team fabricated an L-shaped object made out of the hydrogel and dipped it into a water bath. As the team manipulated the water’s temperature, the gel slowly “walked” forward.

During the tests, the polymer could lengthen or contract, creating a walking movement. What surprised the team was the overall volume of the polymer did not change. In other words, the hydrogel did not take in or expel water during its walk.

A paper on the research was published in the journal Nature on August 10.

The team said in a news statement that the movement process was surprisingly fast with each movement and can change 70 percent of its shape per second.

“Intriguingly, the gel did not change in volume” said author Yasuhiro Ishida. “The substance underwent the change in shape in air and in a liquid environment, showing that it doesn’t require the uptake of water. So in other words, it will work even in a normal air environment.”

“In principle, this hydrogel can walk not only in water, but also in various non-aqueous media including an open-air environment,” Ishida told Gizmag. The L-shaped polymer can continue to walk as long as the heating and cooling cycle is repeated.

Possible applications for the hydrogel include creating artificial muscles that can automatically open and close systems in response to temperature changes, to prevent them from overheating, for instance. Biological applications are also possible.

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